High-efficiency infrared electric liquid-heater

Abstract

An infrared electric liquid heater includes an elongated emitter unit contained within an outer containment tube to define an annular volume through which the to-be-heated water flows. The emitter unit includes a tubular silica-composition envelope that comes into direct contact with the water to be heated. A tungsten filament is contained within the envelope and is supported along the longitudinal axis by spaced-apart filament supports. The envelope is fabricated from a silica composition discovered to provide unique structural properties; the envelope drawn from a melt (by volume) of 99.88% to 99.94% pure silica (SiO 2 ), 0.04% to 0.08% crystalline sodium borax (Na 2 B 4 O 7 .10H 2 ), and 0.2% to 0.04% hydroxide of potassium (KOH). This composition has demonstrated a structural strength that allows for a high efficiency in-line, instant-on heater using only a single silica wall separating the electrically energized filament from the liquid being heated. The interior of the envelope is filled with an argon/krypton/hydrogen bromide gas mixture that re-deposits any metallic vapor arising from the filament back onto the surface of the filament to avoid undesired deposition of the material of the filament onto the inner surface of the envelope. The tungsten filament emits strongly between 1μ and 1.2μ in the near-infrared band. The containment tube is provided with a gold-deposited reflective surface to enhance the overall efficiency of the heater.

What is claimed is: 
     
       1. An infrared electric liquid heater comprising: a conduit for carrying a liquid from an inlet to an outlet;   an infrared radiant emitter contained within said conduit for heating the liquid carried in said conduit;   said emitter having a silica-composition envelope in direct contact with the liquid to be heated and an electrically heated filament sealed within the envelope for providing infrared energy through the envelope into the liquid, said silica-composition drawn from a melt of 99.88% to 99.94% pure silica (SiO 2 ) by volume, 0.04% to 0.08% crystalline sodium borax (Na 2  B 4  O 7 .10H 2 ) by volume, and 0.2% to 0.04% hydroxide of potassium (KOH) by volume, the silica composition having sufficiently high structural strength to remain intact when contacted by cool water when the surface of said envelope is at or above 800° F.   
     
     
       2. The infrared electric liquid heater of claim 1, further comprising an argon, krypton, and hydrogen bromide gas mixture within said envelope. 
     
     
       3. The infrared electric liquid heater of claim 2, wherein said gas mixture comprises: 99.67% to 99.8% argon, 0.1% to 0.15% krypton, and 0.1 to 0.18% hydrogen bromide.   
     
     
       4. The infrared electric liquid heater of claim 1, wherein said filament emits strongly between the 1μ and 1.2μ region of the infrared band. 
     
     
       5. The infrared electric liquid heater of claim 1, wherein said conduit has a diameter between 0.875 inches and 1.5 inches. 
     
     
       6. The infrared electric liquid heater of claim 5, wherein the interior surface of said conduit facing said emitter is conditions to have at least a 95% reflectivity in the infrared band. 
     
     
       7. The infrared electric liquid heater of claim 3, further comprising: end caps for removeably maintaining the conduit and emitter in a concentric liquid-tight relationship.   
     
     
       8. The infrared electric liquid heater of claim 7, wherein said end caps further comprises: a removeable seal of liquid-tight engagement of the end portion of the emitter.   
     
     
       9. The infrared electric liquid heater of claim 8, wherein said removeable seal comprises a chevron seal.